1. Field of the Invention
The present invention relates generally to a channel communication device and a method used in a CDMA communication system, and in particular, to a device and method for generating binary quasi-orthogonal codes and spreading channel signals using the generated binary quasi-orthogonal codes.
2. Description of the Related Art
In general, a CDMA (Code Division Multiple Access) mobile communication system performs channel separation using orthogonal codes in order to increase channel capacity. Walsh orthogonal codes are typically used for the orthogonal codes. For example, a forward link specified by the IS-95/IS-95A standard separates the channels using the Walsh orthogonal codes.
FIG. 1 illustrates the IS-95/IS-95A forward link in which channels are separated by Walsh orthogonal codes. Referring to FIG. 1, channels are separated by unique Walsh orthogonal codes Wi (where i=0 to 63), respectively. The IS-95/IS-95A forward link uses a coding rate R=xc2xd convolutional codes for channel coding, employs BPSK (Binary Phase Shift Keying) modulation for spreading the Walsh orthogonal codes, and has a bandwidth of 1.2288 MHz. Accordingly, the number of available channels is 1.2288 MHz/(9.6 KHz*2)=64. That is, the IS-95/IS-95A forward link can separate 64 channels using the Walsh orthogonal codes.
Therefore, the number of available Walsh orthogonal codes is dependent on the employed modulation method and the minimum data rate. However, future CDMA mobile communication systems will require a greater number of channels assigned to users in order to improve performance. To this end, future CDMA mobile communication systems will employ traffic channels, pilot channels and control channels, thereby increasing channel capacity.
However, there are a limited number of available orthogonal codes available for use. This limitation will restrict the increase in channel capacity. To overcome this disadvantage, it is desirable to generate quasi-orthogonal codes, which will limit interference with the orthogonal codes and a variable data rate.
It is, therefore, an object of the present invention to provide a device and method for generating quasi-orthogonal codes which have the least interference with Walsh orthogonal codes in a CDMA communication system using the Walsh orthogonal codes to perform channel spreading.
It is another object of the present invention to provide a device and method for generating binary quasi-orthogonal codes having excellent full correlation and partial correlation with Walsh orthogonal codes in a CDMA communication system.
It is further another object of the present invention to provide a device and method for spreading channel signals using quasi-orthogonal codes limiting interference with orthogonal codes in a CDMA communication system.
It is still another object of the present invention to provide a channel transmission device and method for spreading channel signals selectively using Walsh orthogonal codes and binary quasi-orthogonal codes in a CDMA communication system.
To achieve the above objects, there is provided a method for generating a binary quasi-orthogonal code in a CDMA communication system. The method comprises generating an m-sequence, and specific left and right sequences having a good full correlation property with the m-sequence; column permuting the specific left and right sequences in a column permutation method used when converting the m-sequence to a Walsh orthogonal code, and connecting the left sequences to the right sequences to generate mask candidates; operating the mask candidates and Walsh orthogonal codes having the same length as the mask candidates to generate quasi-orthogonal code candidate families; and selecting a quasi-orthogonal code out of the generated quasi-orthogonal code candidate families, the selected quasi-orthogonal code satisfying a partial correlation property with the Walsh orthogonal codes, and selecting a mask related to generation of the selected quasi-orthogonal code.